Self-ligating orthodontic brackets comprising a filled and fiber-reinforced polymeric material

ABSTRACT

A self-ligating orthodontic bracket includes a bracket base, an arch wire slot in the bracket base, and a ligation cover. The bracket base and the ligation cover comprise a polymer resin reinforced glass or ceramic fibers, and further comprising a particulate filler. The cover is hingedly connected to the bracket base and rotatable relative to the bracket base between an open, non-ligating position and a closed, ligating position. The combination of reinforcing fibers and filler (e.g., spherical glass particles) provides substantially increased overall strength and durability while providing increased flexibility and toughness in the region of an optional hinge connection between the ligation cover and the bracket base.

RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 10/835,744, filed Apr. 30, 2004 and entitled“SELF-LIGATING ORTHODONTIC BRACKETS COMPRISING A FIBER-REINFORCEDPOLYMERIC MATERIAL,” which is hereby incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention is in the field of orthodontic brackets, moreparticularly to self-ligating orthodontic brackets that include abracket base, at least one slot for receiving an arch wire, and aligation cover. Such brackets comprise a fiber and/orparticle-reinforced polymer material designed for self-ligatingbrackets.

2. The Relevant Technology

Orthodontics is a specialized field of dentistry that involves theapplication of mechanical forces to urge poorly positioned, or crooked,teeth into correct alignment and orientation. Orthodontic procedures canbe used for cosmetic enhancement of teeth, as well as medicallynecessary movement of teeth to correct underbites or overbites. Forexample, orthodontic treatment can improve the patient's occlusion, orenhanced spatial matching of corresponding teeth.

The most common form of orthodontic treatment involves the use oforthodontic brackets and wires, which together are commonly referred toas “braces.” Orthodontic brackets, more particularly the orthodonticbases, are small slotted bodies configured for direct attachment to thepatient's teeth or, alternatively, for attachment to bands which are, inturn, cemented or otherwise secured around the teeth. Once the bracketsare affixed to the patient's teeth, such as by means of glue or cement,a curved arch wire is inserted into the slot of each bracket. The archwire acts as a template or track to guide movement of the teeth intoproper alignment.

There are two distinct classes of orthodontic brackets: those thatrequire the use of ligatures to fasten the arch wire to the bracket, andthose that are self-ligating. In brackets of the first type, smallligature wires or elastic bands are typically used to hold the arch wirein a securely seated position in the brackets. Ligatures or some otherform of fastening means are essential to ensure that the tensioned archwire is properly positioned around the dental arch, and to prevent thewire from being dislodged from the bracket slots during chewing of food,brushing of teeth, or application of other forces. One type ofcommercially available ligature is a small, elastomeric O-ring, which isinstalled by stretching the O-ring around small wings known as “tiewings” that are connected to the bracket body. Metal ligatures are alsoused to retain arch wires within the bracket slots.

In an effort to simplify the process of installing braces, a variety ofself-ligating brackets have been developed. The term “self-ligatingbracket” refers to a class of orthodontic brackets that include somesort of cover, whether separate from or hingedly or slidably attached tothe base, which encloses or otherwise retains the arch wire within theslot of the base. Examples of self-ligating brackets are disclosed inU.S. Pat. Nos. 3,748,740, 4,077,126, 5,857,849, and 6,071,118.

Self-ligating brackets have grown in popularity because of theirconvenient features, but they still exhibit certain disadvantages, notleast of which is that they can be rather fragile if made from polymers.In addition, many polymers can deform (or “creep”) over time, especiallywhen the constant force from an arch wire is applied thereto. Metalbrackets are strong, but have the distinct disadvantage of being lessattractive and providing sharp, jagged, or hard edges that can causeinjury.

Therefore, there exists a need for designs and materials that impartincreased strength and durability to polymeric self-ligating brackets,while also being easy to open and close and easy and inexpensive tomanufacture and install.

BRIEF SUMMARY OF THE PREFFERED EMBODIMENTS

Generally, the orthodontic brackets of the present invention include abracket base, an arch wire slot in the bracket base, and a ligationcover. The cover is hingedly connected to the bracket base and rotatableabout the hinge relative to the bracket base between an open,non-ligating position and a closed, ligating position. The bracket baseand the ligation cover comprise a polymer resin composition reinforcedwith TFG Type 3 glass (“c-glass”) or other appropriate fibers and/orfiller particles, such as spherical glass particles.

The orthodontic bracket is preferably formed as one single piece,requiring no assembly. This reduces the cost and complexity ofmanufacture and prevents unwanted separation of the bracket parts.Although other methods may be used, low cost manufacture is possible byforming the bracket by injection molding.

The brackets of the present invention are self-ligating, i.e., the archwire is clamped or otherwise held between the ligation cover and thebracket base. According to one embodiment, the ligation cover isattached to the base by an elongate film hinge. The cover is rotatableabout the film hinge relative to the bracket base between an open,non-ligating position relative to the arch wire slot and a closed,ligating position relative to the arch wire slot. According to oneembodiment, a curved hinge guide structure may operate in conjunctionwith the film hinge to improve the functionality of the bracket. Inaddition to or instead of the curved structure, a camming structure maybe provided that biases the ligation cover toward the open, non-ligatingposition when the ligation cover is not latched relative to the bracketbase. The ligation cover may advantageously include a latch member thatinteracts with a corresponding recess of the bracket base in order toselectively lock and unlock the cover relative to the base.

An elongate film hinge is characterized by its ability to distributeforces and stresses associated with operation of the hinge along asignificant portion of its entire length. This is in contrast to othertypes of film hinges where the forces and stresses are concentrated atone point or line, which can create a localized area where the filmhinge is more radically stressed and can more easily break. The resultis an improved film hinge that can resist breakage when exposed toshearing and bending forces, such as may occur during placement and useof the orthodontic brackets.

Forming the bracket base and ligation cover of a polymer resincomposition reinforced with c-glass fibers provides increasedflexibility, toughness, and resilience. These characteristics areparticularly beneficial in the area of the hinge(s) connecting theligation cover to the bracket base. Reinforcement with c-glass fibers,which are characterized by relatively small diameters, high flexibility,and short fiber length, results in substantial improvement offlexibility, toughness, and resilience as compared to reinforcement withother materials. Maintaining flexibility of the polymeric material,while providing increased strength and resistance to creep, isparticularly beneficial in the case where an orthodontic bracketincludes a living hinge (e.g., a film hinge) that is expected to flexback and forth several, and often numerous, times during the lifespan ofthe bracket.

According to one embodiment, reinforcing c-glass fibers are preferablyincluded in an amount in a range of about 10% to about 50% by weight ofthe fiber-reinforced polymer resin composition, more preferably in arange of about 15% to about 40% by weight, and most preferably in arange of about 20% to about 35% by weight.

According to one embodiment, the reinforcing c-glass fibers preferablyhave a fiber length less than about 500 microns, more preferably lessthan about 200 microns, and most preferably less than about 100 microns.

According to one embodiment, the reinforcing c-glass fibers preferablyhave a fiber diameter in a range of about 0.5 to about 10 microns, morepreferably in a range of about 1 to about 6 microns, and most preferablyin a range of about 2 to about 4 microns.

According to one embodiment, the reinforcing c-glass fibers preferablyhave an aspect ratio in a range of about 5 to about 200, more preferablyin a range of about 10 to about 100, and most preferably in a range ofabout 20 to about 50.

In addition to, or instead of c-glass fibers, the fiber-reinforcedpolymer resin compositions may include other types of glass or ceramicfibers having similar characteristics of length, diameter and aspectratio.

The polymeric resin may comprise one or more suitable thermoplastic orthermoset resins, including amorphous polymers, crystalline polymers, ora blend of both. Examples of suitable amorphous polymers that may bereinforced with fibers and used to manufacture self-ligating orthodonticbrackets include, but are not limited to amorphous polyamides (e.g.,GRILAMID nylon), acetal polymers, polyetherimides, and polycarbonates.Examples of suitable crystalline polymers include, but are not limitedto, polyarylether ketones (PEEK) and crystalline polyamides (e.g.,TROGAMID nylon).

In addition, the ligation cover may optionally include a bearingprotrusion that aligns with or extends partially into the arch wire slotso as to provide force when the cover is closed in a manner so that thebearing protrusion fixes the arch wire.

According to one embodiment, the polymeric material may also include aparticulate filler that further reinforces the orthodontic bracket.Forming the bracket base and ligation cover of a polymer resincomposition that includes both reinforcing c-glass fibers and a filler(e.g., spherical glass particles) provides even further increasedflexibility, toughness, and resilience. These characteristics areparticularly beneficial in the area of the hinge(s) connecting theligation cover to the bracket base. Inclusion of both glass particlefiller and c-glass reinforcing fibers results in substantial improvementof flexibility, toughness, and resilience throughout the bracket, andparticularly to the hinge area, which requires flexibility andresilience, and the area surrounding the arch wire slot, which requirestoughness and durability. Other exemplary filler particles includeceramic particles, ceramic/glass particles, and organically modifiedceramic particles (e.g., Ormocer).

According to one embodiment, the filler is preferably included in anamount in a range of about 1% to about 30% by weight of the polymerresin composition, more preferably in a range of about 2% to about 20%by weight, and most preferably in a range of about 5% to about 10% byweight.

According to one embodiment, the filler preferably has an averageparticle diameter in a range of about 0.3 to about 30 microns, morepreferably in a range of about 0.5 to about 20 microns, and mostpreferably in a range of about 1 to about 10 microns.

According to one embodiment, the combined total glass content(reinforcing c-glass fibers plus filler) preferably ranges from about10% to about 65% by weight of the filled and fiber-reinforced polymerresin composition, more preferably in a range of about 30% to about 55%by weight, and most preferably in a range of about 40% to about 50% byweight.

These and other advantages and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by references to specific embodiments thereof, which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIGS. 1A-1B illustrate an exemplary self-ligating orthodontic bracketthat can be formed from a polymer resin reinforced with c-glass fibersand/or glass particles;

FIGS. 2A-2B illustrate an exemplary self-ligating orthodontic bracketthat can be formed from a polymer resin reinforced with c-glass fibers,and/or glass particles;

FIGS. 3A-3B illustrate an exemplary self-ligating orthodontic bracketthat can be formed from a polymer resin reinforced with c-glass fibersand/or glass particles; and

FIGS. 4A-4B illustrate an exemplary self-ligating orthodontic bracketthat can be formed from a polymer resin reinforced with c-glass fibersand/or glass particles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Introduction

The orthodontic brackets of the present invention include a bracketbase, an arch wire slot in the bracket base, and a ligation cover. Thecover is hingedly connected to the bracket base and rotatable relativeto the bracket base between an open, non-ligating position and a closed,ligating position. The bracket base and the ligation cover comprise apolymer resin reinforced with c-glass fibers.

II. Reinforcement With C-Glass Fibers

Forming the bracket base and ligation cover from a polymer resinreinforced with c-glass fibers results in an orthodontic bracket havingincreased strength and durability, while exhibiting toughness andflexibility in the region of the hinge connecting the ligation cover tothe bracket base. Toughness and flexibility are importantcharacteristics for a hinged cover of a self-ligating bracket. Strengthand durability are especially useful for the bracket base, particularlythe area of the base surrounding the arch wire slot. Increased strengthand durability helps prevent such an area from becoming deformed ordamaged due to forces transmitted by the arch wire to the arch wireslot. Forming the bracket base and ligation cover from a polymer resinreinforced with c-glass fibers results in increased strength anddurability while exhibiting toughness and flexibility in the region ofthe hinge as compared brackets reinforced with other materials.

C-glass fibers are a preferred class of glass fibers used to reinforcethe polymer resins in forming an orthodontic bracket. C-glass fibers arecharacterized by relatively small diameters, great flexibility, andshort fiber length. Reinforcement with c-glass fibers results insubstantial improvement of flexibility and toughness as compared toreinforcement with other materials. One example of a suitable c-glassfiber is FAMIX 1103-B1, manufactured by Osthoff-Petrasch, located inGermany.

According to one embodiment, the c-glass fibers may be coated with anamino-silane coating, which makes them more compatible when blended withthermoplastic polymers. FAMIX 110.3-B1 is especially formulated forreinforcement within adhesives, plastics, sealants, and resin-basedproducts. When mixed with a molten thermoplastic polymer, slow, forcefulstirring should be maintained while avoiding strong shear forces whichmight cause shortening of the glass fibers.

The physical and chemical properties of FAMIX 1103-B1 are as follows:Color White Density 2.5 g/cc Fiber diameter 3.0-3.2 microns Fiber lengthless than 100 microns Softening temperature 700° C. Applicationtemperature 500° C. Moisture content less than 0.3% Silane content0.3-0.5% Analysis Data Weight Percent SiO₂ 63-66 CaO 4-6 Al₂0₃ 4-5 Fe₂O₃0.43 B₂O₃ 3-6 Na₂O 11-14 K₂O 1.30

According to one embodiment, the reinforcing c-glass fibers arepreferably included in an amount of in a range of about 10% to about 50%by weight of the fiber-reinforced polymer resin composition, morepreferably in a range of about 15% to about 40% by weight, and mostpreferably in a range of about 20% to about 35% by weight.

According to one embodiment, the reinforcing c-glass fibers preferablyhave a fiber length less than about 500 microns, more preferably lessthan about 200 microns, and most preferably less than about 100 microns.

According to one embodiment, the reinforcing c-glass fibers preferablyhave a fiber diameter in a range of about 0.5 to about 10 microns, morepreferably in a range of about 1 to about 6 microns, and most preferablyin a range of about 2 to about 4 microns.

According to one embodiment, the reinforcing c-glass fibers preferablyhave an aspect ratio in a range of about 5 to about 200, more preferablyin a range of about 10 to about 100, and most preferably in a range ofabout 20 to about 50.

Other components, such as fillers, flow additives, and other componentsknown in the art may be added, as desired.

In addition to, or instead of c-glass fibers, the fiber-reinforcedpolymer resin compositions may include other types of glass or ceramicfibers having similar characteristics of length, diameter and aspectratio.

III. Reinforcement With C-Glass Fibers and a Filler

According to one embodiment, the polymeric material may also or insteadinclude a filler that further reinforces the orthodontic bracket.Forming the bracket base and ligation cover from a filled polymer resinreinforced with c-glass fibers results in an orthodontic bracket havingfurther increased strength and durability, while also exhibitingtoughness and flexibility in regions where those characteristics areadvantageous (e.g., an optional hinge connecting the ligation cover tothe bracket base). Strength and durability are especially useful for thebracket base, particularly the area of the base surrounding the archwire slot. Increased strength and durability helps prevent such an areafrom becoming deformed or damaged due to forces transmitted by the archwire to the arch wire slot. Forming the bracket base and ligation coverfrom a polymer resin that is reinforced with both c-glass fibers and aspherical glass particle filler results in further increased strengthand durability while exhibiting toughness and flexibility in the regionof an optional hinge as compared to brackets reinforced only withc-glass fibers.

Spherical glass particles are a preferred type of filler used to furtherreinforce the polymer resins used in forming an orthodontic bracket.Reinforcement with both c-glass fibers and glass particles results insubstantial improvement of flexibility, toughness, strength anddurability as compared to reinforcement with other materials or onlywith c-glass. Since filler particles typically do not increase thestrength and flexibility of materials to which they are added, the factthat glass particles do when added to polymers used to manufactureorthodontic brackets is a surprising and unexpected result. Two examplesof suitable glass fillers include GM27884 and G018-053, bothmanufactured by SCHOTT, located in Germany.

According to one embodiment, the glass particle filler may also becoated with an amino-silane coating, which makes them more compatiblewhen blended with thermoplastic polymers. The physical and chemicalproperties of GM27884 and G018-053 are as follows: GM27884 G018-053Index of Refraction 1.53 1.53 Density (g/cm³) 2.8 2.9 TransformationTemp. (° C.) 630 595 Radio Opacity (mm) 4.2 4.8 Analysis Data WeightPercent Weight Percent SiO₂ ˜55 ˜50 BaO ˜25 ˜30 B₂O₃ ˜10 ˜10 Al₂0₃ ˜10˜10 F — ˜2

Other fillers that may be used include, but are not limited to ceramicparticles, glass/ceramic particles, or organically modified ceramicparticles (e.g., Ormocer), any of which are preferably spherical.

According to one embodiment, the filler is preferably included in anamount in a range of about 1% to about 30% by weight of thefiber-reinforced and filled polymer resin composition, more preferablyin a range of about 2% to about 20% by weight, and most preferably in arange of about 5% to about 10% by weight.

According to one embodiment, the filler preferably has an average (i.e.,d₅₀) particle diameter in a range of about 0.3 to about 30 microns, morepreferably in a range of about 0.5 to about 20 microns, and mostpreferably in a range of about 1 to about 10 microns.

Including a glass particle filler within the fiber reinforced polymerresin composition allows the orthodontic brackets to have a higher totalglass content (resulting in greater strength and durability in theregion of the arch wire slot) without an expected decrease in toughnessand flexibility in the region of an optional hinge. Surprisingly, it hasbeen found that toughness and flexibility increases at the same timethat strength and durability increases.

According to one embodiment, the combined total glass content(reinforcing c-glass fibers plus glass spherical particle filler)preferably ranges from about 10% to about 65% by weight of the filledand fiber-reinforced polymer resin composition, more preferably in arange of about 30% to about 55% by weight, and most preferably in arange of about 40% to about 50% by weight.

IV. Exemplary Polymeric Resin Materials

The polymeric resin may comprise one or more suitable thermoplastic orthermoset resins, including amorphous polymers, crystalline polymers, ora blend of both. Examples of suitable amorphous polymers that may bereinforced with fibers (and optionally a filler) and used to manufactureself-ligating orthodontic brackets include, but are not limited toamorphous polyamides (e.g., GRILAMID nylon, manufactured by EMS-CHEMIEAG, located in Germany), acetal polymers, polyetherimides, andpolycarbonates. Examples of suitable crystalline polymers include, butare not limited to, polyarylether ketones (PEEK) and crystallinepolyamides (e.g., TROGAMID nylon, manufactured by Degussa AG, located inGermany).

V. Exemplary Orthodontic Brackets

A polymer resin reinforced with c-glass fibers (and optionally a filler)may be used to form a self-ligating orthodontic bracket of any design.The following examples are to be considered in all respects only asillustrative and not restrictive. They are intended to give a generalunderstanding of some applications of the present invention.

The orthodontic bracket shown in FIGS. 1A-1B may be manufactured in onesingle piece as an injection molded plastic part from a polymer resinreinforced with c-glass fibers (and optionally a filler). Theorthodontic bracket 100 has a bracket base 110 to which a ligation cover112 is hingedly attached. A slot 114 open to the upper side of thebracket base 110 is provided near the center of said bracket base 110and serves for the insertion of an arch wire 116 therein. An additionalarch wire slot 114 a may also be provided. The arch wire 116, shown witha square cross-section (any other cross section known in the art couldbe used), is arranged inside the slot 114 and serves to correct toothalignment in a known manner.

The ligation cover 112 is hingedly connected to the bracket base 110 byan elongate film hinge 118. The ligation cover 112 is such that it maybe selectively rotated between an open and a closed position relative tothe arch wire slot 114, with the ligation cover, maintaining the archwire 16 within the slot 114 when the ligation cover 112 is in theclosed, ligating position. The elongate film hinge 118 preferably has alength and thickness that are selected so that the hinge 118 has adesired level of flexibility and toughness. Forming the bracket of apolymer resin reinforced with c-glass fibers provides overall increasedstrength and durability while providing increased flexibility andtoughness in the region of the elongate film hinge 118 as compared tobrackets with no fiber reinforcement or reinforcement with fibers thatare substantially stiffer and more rigid than c-glass fibers. Formingthe bracket of a polymer resin reinforced with both c-glass fibers and aglass particle filler provides even further increased flexibility,toughness, strength, and durability.

The film hinge 118 of this embodiment is designed to bend alongsubstantially its entire length rather than at a single point or line.This helps the hinge resist fatigue or fracture better than film hingesthat bend along a single line. The reinforcing c-glass fibers (and anoptional filler) assist the elongate film hinge 118 in remaining elasticand flexible, which helps the hinge 118 to not become fatigued or brokenafter repeated bending.

The bracket embodiment illustrated in FIGS. 1A and 1B preferablyincludes an interactive cam structure 120 with a first curved surface122 and a second curved surface 124. The first curved surface 122interacts with the elongate film hinge 118 to provide a curved surfacethat helps ensure that the elongate film hinge 118 bends gradually overits entire length rather than abruptly at any specific locale. Thesecond curved surface 122 is curved in such a way so that it interactswith a corresponding wall 125 of the base 110 so as to bias the ligationcover 112 toward an open position relative to the bracket base 110 whenthe ligation cover 112 is in the open position. This improves access toarch wire slot 114, making insertion or removal of the arch wire 116easier. The second curved surface 124 may, depending on the shape of thecorresponding wall 125 of the bracket base 110, also act to bias theligation cover 112 to remain in a closed position when in the closedposition relative to the bracket base 110.

An angled keyway 126 is provided near one end of the base 110. Theligation cover contains a corresponding locking tongue 128 that enablesthe ligation cover 112 to be selectively locked or unlocked relative tothe bracket base 110. The ligation cover 112 is locked to bracket base110 (as seen in FIG. 1B) by closing the ligation cover so that thelocking tongue 128 is inserted into angled keyway 126.

In the event that the arch wire 116 pushes against the ligation coverwith sufficient force to cause the cover to bulge upwardly relative tothe bracket base 110, rather than causing the tongue 128 to withdrawfrom the angled keyway 126, which could result in undesireddisengagement of the ligation cover, the locking tongue 128 is insteadpulled more deeply into the angled keyway 126, thereby tightening thelocking mechanism. This provides added safety, and in order to open thecover, the locking tongue 128 is pulled out of angled keyway 126 andover an outer protrusion 129 of the bracket base 110.

Furthermore, a bearing protrusion 130 is provided at the inside andmiddle of the ligation cover to assist in fixing the arch wire 116 inthe slot 114 while the ligation cover is in the closed state (FIG. 1B).The bearing protrusion 130 reduces the play in the system by effectivelywidening the ligation cover 112 in the vicinity of the arch wire slot114.

FIGS. 2A and 2B depict an alternative embodiment of an orthodonticbracket 200 according to the invention that does not include a camstructure. Instead, the orthodontic bracket 200 depicted in FIGS. 2A and2B includes a bracket base 210 and a ligation cover 212 attached to thebracket base 210 by means of an elongate film hinge 218. The bracketalso includes an angled keyway 226, a locking tongue 228, and a bearingprotrusion 230. The bracket base 210 further includes a curved end 232that acts as a hinge guide in order to cause the elongate film hinge 218to bend gradually over a significant portion of its entire length. Inthis way, the curved end 232 of the bracket base 210 acts in similarmanner to the curved hinge-guiding surface 122 of the cam structure 120of the orthodontic bracket 100 depicted in FIGS. 1A-1B. Thus, as theligation cover 212 is moved from an open, non-ligating position (FIG.2A) to a closed, ligating position (FIG. 2B), the elongate film hinge218 at least partially abuts the curved end 232. The abutment betweenthe elongate film hinge 218 and the curved end 232 causes the elongatefilm hinge 218 to bend gradually around the curved end 232 so as tobetter distribute the bending forces and bending angles alongsubstantially the entire length of the elongate film hinge 218.

FIGS. 3A and 3B illustrate an alternative bracket embodiment that canalso be formed from a polymer resin reinforced with c-glass fibers (andoptionally a filler). Bracket 300 is similar to the bracket illustratedin FIGS. 1A-1B in that it includes a bracket base 310, a ligation cover312, a slot 314, an arch wire 316 (seen in FIG. 3B), an angled keyway326, a locking tongue 328, and a bearing protrusion 330. This examplediffers from the bracket illustrated in FIGS. 1A-1B in that although italso uses a film hinge 318 to attach the ligation cover 312 to thebracket base 310, the hinge 318 is not as elongate as hinge 118 shown inFIGS. 1A-1B. Bracket 300 may further include additional arch wire slots334 and 336 for use with additional or alternative arch wires as knownin the art. Reinforcing c-glass fibers provide overall increasedstrength and durability while providing increased flexibility andtoughness in the region of the film hinge 318. Including both c-glassfibers and a glass particle filler provides even further increasedflexibility, toughness, strength, and durability.

FIGS. 4A and 4B illustrate an alternative bracket embodiment that canalso be formed from a polymer resin reinforced with c-glass fibers (andoptionally a filler). Bracket 400 includes a bracket base 410, aligation cover 412, a slot 414, an arch wire 416 (seen in FIG. 4B), amain film hinge 418, an angled keyway 426, a locking tongue 428, abearing protrusion 430, and an additional arch wire slot 434. Thisexample differs from that illustrated in FIGS. 3A-3B in that it furtherhas a spring element 438 attached at one end of the bracket base 410 bya film hinge 440 and at an opposite end to the ligation cover 412 by afilm hinge 442. Reinforcing c-glass fibers provide overall increasedstrength and durability while providing increased flexibility andtoughness in the region of the film hinges 418, 440, 442, and springelement 438. Including both c-glass fibers and a glass particle fillerprovides even further increased flexibility, toughness, strength, anddurability.

Various other bracket designs are disclosed in U.S. Pat. No. 6,607,383;U.S. application Ser. No. 09/914,737, filed Aug. 29, 2001, abandoned;and U.S. application Ser. No. 09/953,400, filed Sep. 12, 2001. Forpurposes of disclosing exemplary orthodontic bracket designs, theforegoing U.S. applications and patent are incorporated by reference.

The following comparative test results illustrate the advantages offorming an orthodontic bracket from a polymer resin reinforced withc-glass fibers, and the increased advantage of further including a glassparticle filler.

EXAMPLE 1

An orthodontic bracket is formed by injection molding an acetalthermoplastic resin. The bracket design is the same as that illustratedin FIGS. 1A and 1B. No reinforcing glass fibers are used in molding thebracket. When used in an orthodontic procedure, the acetal thermoplasticpolymer resin experiences deformation. In addition, although the hingeis very flexible, it is prone to breakage when a shearing force isapplied to the ligation cover.

EXAMPLE 2

An orthodontic bracket is formed by injection molding an acetalthermoplastic resin reinforced with c-glass fibers. The bracket designis the same as that illustrated in FIGS. 1A and 1B. The concentration ofc-glass fibers is 30% by weight of the overall bracket. When used in anorthodontic procedure, the c-glass reinforced orthodontic bracketsbetter resists deformation than the bracket of Example 1. Moreover, thehinge is much stronger, and thus sufficiently flexible to bendrepeatedly while opening and closing the ligation cover.

EXAMPLE 3

A hypothetical orthodontic bracket is formed by injection molding anacetal thermoplastic resin reinforced with c-glass fibers and glassspherical particle filler. The bracket design is the same as thatillustrated in FIGS. 1A and 1B. The concentration of c-glass fibers is35% by weight of the overall bracket. The concentration of glassparticle filler is 10% by weight of the overall bracket, such that thetotal glass concentration (fibers plus filler) is 45% by weight. Whenused in an orthodontic procedure, the filled and c-glass reinforcedorthodontic brackets better resist deformation than the brackets ofExamples 1 and 2. Moreover, the hinge is even more durable than that ofExample 2, and thus sufficiently flexible to bend repeatedly whileopening and closing the ligation cover.

EXAMPLE 4

A hypothetical orthodontic bracket is formed by injection molding anylon thermoplastic resin (e.g., TROGAMID or GRILAMID) reinforced withc-glass fibers. The bracket design is the same as that illustrated inFIGS. 1A and 1B. The concentration of c-glass fibers is 35% by weight ofthe overall bracket. When used in an orthodontic procedure, the hingeexhibits sufficient flexibility for use, although it is shows crazingafter repeated opening and closing of the ligation cover. After many(e.g., 50) opening and closing cycles, the ligation cover willeventually separate from the bracket base.

EXAMPLE 5

A hypothetical orthodontic bracket is formed by injection molding anylon thermoplastic resin (e.g., TROGAMID or GRILAMID) reinforced withc-glass fibers and glass spherical particle filler. The bracket designis the same as that illustrated in FIGS. 1A and 1B. The concentration ofc-glass fibers is 35% by weight of the overall bracket. Theconcentration of glass particle filler is 10% by weight of the overallbracket, such that the total glass concentration (fibers plus filler) is45% by weight. When used in an orthodontic procedure, the filled andc-glass reinforced orthodontic brackets are even more deformationresistant than the bracket of Example 4. Moreover, the hinge is evenmore durable than that of Example 4, and thus sufficiently flexible tobend repeatedly while opening and closing the ligation cover withoutcrazing. Even after hundreds of opening and closing cycles, the ligationcover still remains attached to the bracket base.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. An orthodontic bracket comprising: a bracket base; at least one archwire slot in said bracket base, said slot being adapted to receive anarch wire therein; and a ligation cover that can be selectively movedrelative to the bracket base between an open, non-ligating positionrelative to the arch wire slot and a closed, ligating position relativeto the arch wire slot; wherein the bracket base and ligation covercomprise a filled polymer resin composition reinforced with glass orceramic fibers and a particulate filler.
 2. An orthodontic bracket asrecited in claim 1, wherein the particulate filler comprises at leastone of glass particles; ceramic particles, ceramic/glass particles, ororganically modified ceramic particles.
 3. An orthodontic bracket asrecited in claim 2, wherein the particulate filler comprises sphericalparticles.
 4. An orthodontic bracket as recited in claim 1, wherein theparticulate filler is included in an amount in a range of about 1% toabout 30% by weight of the polymer resin composition.
 5. An orthodonticbracket as recited in claim 1, wherein the particulate filler isincluded in an amount in a range of about 2% to about 20% by weight ofthe polymer resin composition.
 6. An orthodontic bracket as recited inclaim 1, wherein the particulate filler is included in an amount in arange of about 5% to about 10% by weight of the polymer resincomposition.
 7. An orthodontic bracket as recited in claim 1, whereinthe particulate filler includes particles having an average diameter ina range of about 0.3 to about 30 microns.
 8. An orthodontic bracket asrecited in claim 1, wherein the particulate filler includes particleshaving an average diameter in a range of about 0.5 to about 20 microns.9. An orthodontic bracket as recited in claim 1, wherein the particulatefiller includes particles having an average diameter in a range of about1 to about 10 microns.
 10. An orthodontic bracket as recited in claim 1,wherein the polymer resin composition is reinforced with c-glass fibers.11. An orthodontic bracket as recited in claim 1, wherein the polymerresin comprises at least one of a polyetherimide, a polycarbonate resin,a polyaryletherketone resin, a polyamide resin, a crystalline polyamide,or an amorphous polyamide.
 12. An orthodontic bracket as recited inclaim 1, wherein the reinforcing fibers are included in an amount in arange of about 10% to about 50% by weight of the polymer resincomposition.
 13. An orthodontic bracket as recited in claim 1, whereinthe reinforcing fibers are included in an amount in a range of about 15%to about 40% by weight of the polymer resin composition.
 14. Anorthodontic bracket as recited in claim 1, wherein the reinforcingfibers are included in an amount in a range of about 20% to about 35% byweight of the polymer resin composition.
 15. An orthodontic bracket asrecited in claim 1, wherein the bracket base and ligation cover areformed together as a single integral piece.
 16. An orthodontic bracketcomprising: a bracket base; at least one arch wire slot in said bracketbase, said slot being adapted to receive an arch wire therein; aligation cover hingedly connected to the bracket base and selectivelyrotatable relative to the bracket base between an open, non-ligatingposition and a closed, ligating position; and an elongate film hingeattached at one end to the bracket base and at an opposite end to theligation cover so as to hingedly connect the ligation cover to thebracket base, wherein the bracket base, ligation cover, and film hingecomprise a polymer resin composition reinforced with substantiallyspherical filler particles comprising at least one of glass, ceramic,ceramic/glass, or organically modified ceramic particles.
 17. Anorthodontic bracket as recited in claim 16, wherein the filler particlescomprise spherical glass particles.
 18. An orthodontic bracket asrecited in claim 16, wherein the polymer resin composition is furtherreinforced with at least one of glass or ceramic fibers.
 19. Anorthodontic bracket comprising: a bracket base; at least one arch wireslot in said bracket base, said slot being adapted to receive an archwire therein; and a ligation cover hingedly connected to the bracketbase and selectively rotatable relative to the bracket base about ahinge element between an open, non-ligating position and aclosed-ligating position; wherein the bracket base and ligation covercomprise a polymer resin reinforced with spherical glass fillerparticles.
 20. An orthodontic bracket as recited in claim 19, whereinthe polymer resin composition is further reinforced with at least one ofglass or ceramic fibers.